Two drugs commonly prescribed to Alzheimer's patients to treat depression show no benefit yet may cause side effects such as nausea and drowsiness, research has shown.
A study found that sertraline and mitazapine were no more effective than an inactive placebo.
Researchers said the findings should lead to a rethink about the way Alzheimer's-related depression is treated.
A total of 326 patients from nine centres in England were recruited for the study and allocated either one of the antidepressants or a placebo.
After 13 weeks, decreases in depression measurement scores did not differ between the three groups.
Around a quarter fewer patients taking the placebo had adverse reactions, such as nausea and drowsiness.
The research, led by Professor Sube Banerjee from the Institute of Psychiatry, King's College London, was reported in an online edition of The Lancet medical journal.
The authors wrote: "Clinicians and investigators need to reframe the way they think about the treatment of people with Alzheimer's disease who are depressed, and reconsider routine prescription of the antidepressants."